Avoidance of redundant signaling in multi-layer video bitstreams

Abstract

A method of decoding includes receiving a bitstream having a plurality of layers and a video parameter set (VPS), where the VPS includes a direct reference layer flag, where the direct reference layer flag equal to a first value specifies that a second layer is not a direct reference layer for a first layer, and where the direct reference layer flag equal to a second value specifies that the second layer is the direct reference layer for the first layer; deriving a reference layer flag by: initially setting the reference layer flag to the first value; and updating the reference layer flag to the second value when the direct reference layer flag has the second value; and decoding a picture from the first layer in accordance with the reference layer flag to obtain a decoded picture.

What is claimed is: 
     
         1 . A non-transitory computer-readable storage medium storing instructions that, when executed by one or more processors, cause a video processing apparatus to:
 receive a bitstream having a plurality of layers and a video parameter set (VPS), wherein the VPS includes a direct reference layer flag (vps_direct_ref_layer_flag), wherein the direct reference layer flag equal to 0 specifies that a second layer j is not a direct reference layer for a first layer i, and wherein the direct reference layer flag equal to 1 specifies that the second layer j is the direct reference layer for the first layer i;   derive a reference layer flag (LayerUsedAsRefLayerFlag[j]) by:
 initially setting the reference layer flag to 0; and 
 updating the reference layer flag to 1 when the direct reference layer flag is equal to 1; and 
   decode a picture from the first layer i in accordance with the reference layer flag to obtain a decoded picture,   wherein the reference layer flag specifies whether a layer with a layer index j is used as a reference layer by any other layer.   
     
     
         2 . The non-transitory computer-readable storage medium of  claim 1 , wherein an index value of [i] is in a range of zero to vps_max_layers_minus1. 
     
     
         3 . The non-transitory computer-readable storage medium of  claim 1 , wherein vps_max_layers_minus1 plus 1 specifies a number of layers specified by the VPS. 
     
     
         4 . The non-transitory computer-readable storage medium of  claim 1 , further comprising displaying the decoded picture on a display of an electronic device. 
     
     
         5 . A method of encoding implemented by a video encoder, the method comprising:
 setting a direct reference layer flag (vps_direct_ref_layer_flag) equal to 0 to specify that a second layer j is not a direct reference layer for a first layer i, and to 1 to specify that the second layer j is the direct reference layer for the first layer i, wherein the direct reference layer flag is configured for use in derivation of a reference layer flag (LayerUsedAsRefLayerFlag[j]), wherein the reference layer flag specifies whether a layer with a layer index j is used as a reference layer by any other layer;   generating a video parameter set (VPS) including the direct reference layer flag; and   encoding the VPS into a video bitstream.   
     
     
         6 . The method of  claim 5 , wherein an index value of [i] is in a range of zero to vps_max_layers_minus1, wherein vps_max_layers_minus1 plus 1 specifies a number of layers specified by the VPS, which is a maximum allowed number of layers in each coded video sequence (CVS) referring to the VPS. 
     
     
         7 . The method of  claim 5 , further comprising deriving the reference layer flag and performing, by a hypothetical reference decoder (HRD) of the video encoder, a conformance test on the video bitstream using the reference layer flag, wherein the reference layer flag is derived by:
 initially setting the reference layer flag to 0; and   updating the reference layer flag to 1 when the direct reference layer flag is equal to 1.   
     
     
         8 . The method of  claim 5 , further comprising transmitting the video bitstream toward a video decoder. 
     
     
         9 . A non-transitory computer-readable storage medium storing instructions that, when executed by one or more processors, cause a video processing apparatus to:
 receive a bitstream having a plurality of layers and a video parameter set (VPS), wherein the VPS includes a direct reference layer flag (vps_direct_ref_layer_flag), wherein the direct reference layer flag equal to 0 specifies that a second layer j is not a direct reference layer for a first layer i, and wherein the direct reference layer flag equal to 1 specifies that the second layer j is the direct reference layer for the first layer i; and   derive a reference layer flag (LayerUsedAsRefLayerFlag[j]) by:
 initially setting the reference layer flag to 0; and 
 updating the reference layer flag to 1 when the direct reference layer flag is equal to 1; and 
   decode a picture from the first layer i in accordance with the reference layer flag to obtain a decoded picture,   wherein the reference layer flag specifies whether a layer with a layer index j is used as a reference layer by any other layer.   
     
     
         10 . The non-transitory computer-readable storage medium of  claim 9 , wherein the instructions further cause the video processing apparatus to display the picture as decoded. 
     
     
         11 . A non-transitory computer-readable storage medium storing an encoded bitstream and one or more instructions that, when executed by at least one processor, cause a decoding device to generate a video based on the encoded bitstream, the encoded bitstream comprising:
 a direct reference layer flag (vps_direct_ref_layer_flag) set equal to 0 to specify that a second layer j is not a direct reference layer for a first layer i, and to 1 to specify that the second layer j is the direct reference layer for the first layer i, wherein the direct reference layer flag is configured for use in derivation of a reference layer flag (LayerUsedAsRefLayerFlag[j]), and wherein the reference layer flag specifies whether a layer with a layer index j is used as a reference layer by any other layer; and   a video parameter set (VPS) including the direct reference layer flag.   
     
     
         12 . The non-transitory computer-readable storage medium of  claim 11 , wherein the first layer has an index value of [i] and the second layer has an index value of [j], wherein the index value of [i] is in a range of zero to vps_max_layers_minus1. 
     
     
         13 . The non-transitory computer-readable storage medium of  claim 12 , wherein vps_max_layers_minus1 plus 1 specifies a number of layers specified by the VPS, which is a maximum allowed number of layers in each coded video sequence (CVS) referring to the VPS.